@kurup
Believe me,the topic of warhead specifications is so secret that any academic exercise to determine the payload can at best be described as speculative! Not even folks working on K4 would know the exact specification of the warheads it'll carry. Based on speculative analysis,and some of the published papers,one can say that K-4 has been designed with single warhead in mind and the range is 3500-4000kms.
K-5 will be india's true SLBM with 3 MIRVs and 6000+ kms range,now how will they achieve this?-it is an elaborate process involving optimization at various fronts ranging from
1)casing(composites instead of maraging steel)
2)newer high energy materials with higher specific impulse,
3)miniaturization of MEMS based sensors and actuators,
4)light weight reaction control systems etc.
with#1 and #2 contribute a lot in weight reduction of missiles,but that is not to say that #3 and #4 are insignificant.
One significant challenge with #1 is that with increased diameter strategic missiles the stresses acting radially on the casing is very high due to chamber pressure hence a thick walled maraging steel structure is prefered,but that increases weight significantly,hence the choice of an appropriate composite structure that can withstand high chamber pressure of first stage in our A5 system was a challenge that they painstakingly overcame.This will be implemented in newer missiles and will be called A6.
A6 is basically a highly optimized A5 with a host of improvements that render it a new missile altogether!
Another challenge with #2 is the type of solid fuel,as you know the shelf life of any missile is directly contingent upon the physical properties of the solid fuel.With canisterized A5 and A6 coming into picture,newer HTPB+AP compositions must be found that can hold the structural integrity for the required shelf life.
Now one would ask,why is structural integrity of solid propellants so important?Well the answer lies in the uniform burning or so called "regression rate-r" of solid propellants inside the missile.Any deformation in the surface would lead to significant increase in rate of burning and hence the chamber pressure.With age,the solid propellants are subjected to bending loads inside the missile due to gravity- this might develop minor cracks and crack provides extra surface area for burning- this in turn creates irregular regression rate and increased chamber pressure than desired.If allowed to go unabated,the chamber pressure might increase beyond the mechanical tolerances of the missile casing- especially during the initial phases when the thrust builds up very rapidly.
I'd also like to mention that in this regard russians are way ahead of us!
These few topics that i touched upon are very essential from the design aspect of a SLBM as well. If you are interested in detailed technical discussion,feel free to contact me!
Thanks in advance
Amardeep Mishra